The conantokin-like peptide superfamily is a distinctive group of Conus peptides. Conformational stability of the conantokin-like peptides is not achieved through multiple disulfide crosslinks, but rather by post-translational modification. Glutamate residues that are spaced every three or four amino acids are modified to gamma-carboxyglutamate (Gla); this motif would stabilize a helical conformation in the extracellular environment through chelation of Ca++. One branch of the conantokin-like superfamily comprises the only peptidic ligands known to be targeted to N-methyI-D-aspartate (NMDA) receptors. The broad focus of the proposed work is to identify the members of the conantokin-like peptide superfamily that are targeted to NMDA receptors, and to evaluate the subtype selectivity of peptides in the superfamily that do target NMDA receptors. Since several conantokins (e.g., conantokin-G and conantokin-R) have previously been shown to be potent anticonvulsants, we plan to correlate NMDA receptor subtype selectivity of an individual conantokin to the anticonvulsant efficacy observed. The goal is to understand the underlying mechanisms of the unusually favorable protective index afforded by the conantokin peptides when tested in an animal model, the Fring's audiogenic seizure mouse. A longer-term objective is a functional characterization of the branches of the conantokin-like peptide superfamily that do not target NMDA receptors.